The present invention is concerned with an aircraft fuel tank vent. More specifically, the present invention is concerned with a combined fuel tank vent protector and overpressure device.
Aircraft fuel tanks need to be vented to the atmosphere in use. Increasing and decreasing fuel levels due to fuelling and fuel consumption respectively means there is a variable volume of the tank in and out of which air needs to be able to flow. If air were not able to flow in and out of this volume, fuel entry into, and exit from, the tank would be impeded.
Furthermore, as the aircraft's altitude changes, variations in local atmospheric pressure need to be accounted for to prevent a large, undesirable pressure differential across the skin of the fuel tanks.
Still further, there is a possibility that during fuelling of the tanks they will overflow. In this case the fuel must be able to flow freely from the tank without causing excessive pressure within the fuel tank.
In order to allow flow in and out of the tanks, vents are provided. Such vents are commonly provided with vent protector devices disposed between the vent and the tank. Vent protectors comprise a duct in communication with the tank exterior, which may comprise one or more bends. They may contain other components to ensure that only air, vapour and fuel can pass between the tank and the exterior.
Such vent protector devices may possibly, under certain rare conditions, become blocked.
In order to overcome the problem of blockage overpressure devices have been developed which form an alternative path from the tank to the atmosphere. The overpressure devices do not permit flow under normal operating conditions of the vent protector. However, when the vent protector becomes blocked, the overpressure device is activated and allows passage of fluid in or out of the tank.
In some aircraft fuel tank designs the overpressure device is designed to operate even if the vent protector is not blocked. In these designs the overpressure device will operate to prevent excessive positive or negative pressure differentials between the inside and outside of the tank. These pressures may arise due to fuel overflow during fuelling or a rapid ascent or descent during flight. In any case, the overpressure devices are arranged to prevent excessive pressure differentials from forming between the tank and the exterior.
In known systems, the vent protector and overpressure device are separate components, requiring two penetrations of the fuel tank. This is undesirable for fuel tanks positioned near flight surfaces (e.g. in the wing) because wing skin penetrations create undesirable noise effects and reduce aerodynamic efficiency.